GB2354321A

GB2354321A - Geodetic device with a laser arrangement

Info

Publication number: GB2354321A
Application number: GB0020139A
Authority: GB
Inventors: Bernd Donath; Wieland Feist; Christian Graser; Ludwin-Heinz Monz
Original assignee: ZSP Geodaetische Systeme GmbH
Current assignee: Trimble Jena GmbH
Priority date: 1999-08-27
Filing date: 2000-08-17
Publication date: 2001-03-21
Anticipated expiration: 2020-08-17
Also published as: GB0020139D0; JP2001082960A; SE0002920L; US6411372B1; CH694669A8; SE520543C2; CH694669A5; GB2354321B; DE19941638C1; SE0002920D0

Abstract

The invention relates to a geodetic device 1 which is placed with the aid of a stand 3 over a ground mark 4 wherein its telescope can pivot about a tilt axis KA and an axis of rotation DA and which is equipped with a laser arrangement which is used to centre the axis of rotation DA over the ground mark 4 and to determine the height h of the point of intersection S of the tilt axis KA and the axis of rotation DA above the ground mark 4. A first, preferably collimated laser beam 10 extending in the axis of rotation DA is provided and also at least one further laser beam path 11 which diverges with respect to the first laser beam 10 defining an angle q . The device further comprises a measuring device for determining the distance a between two laser beam paths at the ground mark 4 and also an evaluating device for calculating the height h of the point of intersection S above the ground mark.

Description

2354321

DESCRIPTION

GEODETIC DEVICE WITH A LASER ARRANGEMENT The invention relates to a geodetic device of the type having a telescope F, whose sighting axis ZA has a common point of intersection S with a tilt axis KA and an axis of rotation DA about which the telescope F can pivot and wherein ftirthermore a laser arrangement is provided which serves to align the axis of rotation DA over the ground mark and to detennine the height h of the point of intersection S above the ground mark.

Geodetic devices of this type, such as, for example, theodolites or tachymeters, are known. They are used for land surveying on the basis of determining horizontal and vertical angle measurements and for this purpose are generally erected with the aid of a stand, for example, above a limit marking. In principle, they consist of an upper part which can pivot about the perpendicularly aligned axis of rotation DA (often also referred to as the vertical axis) and which supports a telescope which can transit about the tilt axis KA and comprises cross-lines and a range adjustment in a sighting axis ZA which, like the axis of rotation DA and the tilt axis KA, intersects the point of intersection S Thus, for example, DE 38 38 512 describes a theodolite where the stand carrier plate which supports the theodolite comprises in its centre a cut- out through which it is possible to direct a laser beam along the axis of rotation onto the ground mark with which the theodolite is to be aligned. As a consequence, an optical sighting device is produced which facilitates the erection and alignment.

However, this arrangement of the device is not sufficient to provide extremely precise measurements and it is also necessary to provide in addition information regarding the height of the instrument, i.e. the height h of the point of intersection S of the sighting axis, ZA, tilt axis KA and axis of rotation DA above the ground mark.

In this respect DE 198 02 379 Al illustrates a measuring device which has different types of accessories, including also aids to determine the height of the instrument. For this purpose, a prism is to be placed on the ground mark and a supplementary mirror pivoted in ftont of the telescope which comprises a horizontally aligned sighting axis, so that the distance to the ground mark can be measured using the electro-optical distance measuring device and in this manner the instrument height can be determined.

2 Furthermore, DE 40 07 245 A I describes a "Device for centring a geodetic Instrument" over a defined ground mark with the aid of an optical sighting device which is disposed centrally with respect to the vertical axis of the instrument, wherein this sighting device again, as described above, comprises means for producing a visible collimated laser beam bundle and means for projecting the bundle onto the ground mark lying in the extension of the vertical axis of the geodetic instrument. However, in this case, it is also proposed to use the laser beam bundle to measure the height between the ground mark and the sighting axis.

The description relating to this merely discloses that the laser beam bundle is modulated, the light reflected by the ground mark is directed to the receiving device and the distance between the ground mark and the sighting axis is determined in an evaluating device connected downstream, wherein the distance between the ground mark and the sighting axis is concluded from the receiving signal. Distance measuring devices of this type have the disadvantage that they are expensive to produce and therefore cost-intensive.

An object of the present invention is to develop further a geodetic instrument of the type mentioned in the introduction so that it is guaranteed that the device can be centred and also that the height of the point of intersection of the sighting axis, pivot axis and axis of rotation above the ground mark can be deter-mined with a small outlay as far as the device is concerned whilst maintaining a high level of accuracy and in an ergonomically favourable manner.

In accordance with the invention there is provided a first, preferably collimated, laser beam extending in the axis of rotation DA, and at least one further laser beam path which diverges with respect to the first laser beam, which include between the two an angle y; furthermore there are provided a measuring device for determining the distance a between two laser beam paths at the height of the ground mark and an evaluating device for calculating the height h of the point of intersection S above the ground mark from the relationship h-a when the angle y is known. The distance a is measured in the horizontal, i.e. at a right angle to the axis of rotation DA.

It is possible using this arrangement to determine the distance between the ground mark and the point of intersection S on the basis of a measuring triangle which is formed from the first collimated laser beam, at least one further laser beam path, which includes with 3 the first laser beam a preferably constant angle y, and the distance a. This relationship h- a corresponds to an elementary function of trigonometry.

The essential advantage of the invention resides in the possibility of a structure which has a relatively low expenditure as far as the device is concerned owing to the fact that fewer components are required than for a device which is equipped according to the prior art with an optoelectronic distance measuring device.

One advantageous embodiment of the laser arrangement provides a housing which is disposed with its longitudinal axis in a radial manner with respect to the axis of rotation DA, a laser disposed in the housing, a lens which is likewise disposed in the housing for the purpose of bundling the laser beams and a deflecting element disposed downstream of the lens outside the housing for coupling the laser beam into the axis of rotation DA; ftirthermore the laser arrangement comprises optical means to generate the diverging laser beam path.

Different options are feasible for arranging the latter optical means, which can, for example, be designed such that a diff-racting element comprising an optically effective structure is placed in the first laser beam causing a portion of this beam to be transformed into a circular diffraction pattern which is aligned in a concentric manner with respect to the axis of rotation DA and is directed in a diverging manner at the ground mark or its surrounding area.

The diffracting element is disposed upstream or downstream of the deflecting element in the beam path and consists of a transparent plate which is provided with a structure hologram. The structure hologram is formed ftorn geometric shapes, preferably dots which are arranged in a circle, in a line and/or in two-dimensional rows. These patterns are disposed centrally with respect to the laser beam and have maximum brightness in their centre.

This maximum brightness can be formed by a central area section which has the highest possible transparency or also by a central cut-out in the transparent plate.

As an alternative to the aforementioned embodiment it is also possible for the purpose of generating the diverging laser beam path to provide at least one fin-ther laser light source which directs beams at an angle aO' into the lens and is imaged by the lens onto the ground mark or its surrounding area, wherein the beam path directed at the ground mark includes with the first beam path the diverging angle y which is proportional to the angle a of the incoming beams.

4 In this respect, a particularly preferred embodiment of the invention resides in the fact that a first laser diode is disposed in such a manner that the beam issuing therefrom is directed into the lens in the direction of the optical axis, i.e. at an angle of a=O', wherein the light emitted by the laser diode serves to generate the first laser beam and thus serves primarily to centre the geodetic device.

In addition to this first laser diode, two fimilier laser diodes are provided from which beams are directed at an angle of at-O', preferably a=10' into the lens.

The two laser diodes which direct beams into the lens at the angle at-O' generate two laser beams which include with the first laser beam in each case a diverging angle y. As a consequence, each of the three laser light sources is imaged on the ground mark or its close surrounding area, wherein the three laser diodes are disposed with reference to the lens in such a manner that their three images lie in a straight line. The centre image is then used for centring purposes and when the angle y is known the distances a of the two outer images to the centre image is a measurement for the height h of the point of intersection S above the ground mark.

It goes without saying that addition constants can also be used to determine this height h, which constants are obtained, for example, by means of the height difference, produced by the device used, between the vertex of the diverging beam paths and the point of intersection S.

As an alternative, the measuring device can be a scale which is designed such that it is possible to read off the distance a or the total 2a visually and is provided with a line marking which is gauged in a length unit or the measuring device can be a position-sensitive optoelectronic detector with a downstream evaluating and display device.

The scale is used to determine the distance a in a convenient manner, in that the scale is placed on the ground mark, namely in such a manner that the first laser beam and the imaging of the first beam source is directed at the line marking and then with the aid of the line marking the diameter d=2a of the circular diff-raction pattern or the distances a of the images of the second and third beam source are read from the image of the first beam source.

According to a particularly advantageous embodiment of the invention, the line marking ( the angle y being constant) is calibrated differently to the metric unit in such a manner that a value for the height h is immediately available visually.

The position-sensitive detectors can be, for example, CCD lines or CCD arrays. The maximum distance between two beam sources imaged on the array or on the CCD line is an equivalent for the height h, a prerequisite likewise being that the three images lie on a straight line.

It is possible, ftorn the maximum distance 2a. of the two outer images on the detector, to obtain a value for the height h using a signal processing procedure known per se and this value is displayed on a display. In an advantageous manner, a CCD line and an indicator display can be accommodated to form a compact unit, for example, in the form of a flat measuring instrument.

In order to detennine the height h it is then merely necessary to place this flat measuring instrument on the ground mark, ensuring that the first laser beam strikes the CCD line and also the two outer beam paths are imaged on the CCD line, whereupon a value for the height h can then be read off directly from the display.

For the sake of completeness, it should be mentioned that the beam. sources or the laser diodes emit beams in the visible wave length range of light with an intensity which is easily recognisable even when superimposing daylight.

The invention is explained in detail hereinunder, by way of example only, with reference to an exemplified embodiment and the associated drawings, in which:

Figure I is a schematic illustration of the entire geodetic device, Figure 2 shows a first variant of the measuring principle to determine the height h; Figure 3 shows a second variant of the measuring principle to determine the height h; Figure 4 shows an example of a reading scale; and Figure 5 shows an example for a measuring and display instruction with a CCD line.

Referring to Figure 1, a geodetic device 1 with a three-screw levelling base 2 is placed on a stand 3 and centred over a ground mark 4.

6 The geodetic device I comprises, for example, a theodolite, whose telescope F can pivot about a tilt axis KA and an axis of rotation DA. The tilt axis KA and the axis of rotation DA both intersect the sighting axis ZA of the telescope F which in Figure I is perpendicular to the drawing plane and for this reason appears only as a dot in a point of intersection S.

As a prerequisite for precise measurements which are to be performed using the sighting axis ZA, it must be possible to align the device 1 exactly above the ground mark 4. The device I is then aligned if the tilt axis KA is aligned horizontally and the axis of rotation DA is aligned perpendicularly with the ground mark 4.

The alignment process is assisted, for example, by a bubble level [not illustrated in the drawing], which is disposed on the device I and also a laser arrangement which consists essentially of a housing 5, which is disposed with its longitudinal axis 6 in a radial manner with respect to the axis of rotation DA, at least one laser beam source, for example, a laser diode 7.1 which emits beams in the visible wave length range, a lens 8 through which the laser beams are bundled and are directed to a deflecting element 9 which ensures that the laser beam 10 is deflected out of the longitudinal axis 6 into the axis of rotation DA.

It is now frequently necessary during the measuring process to also take into consideration the height h of the point of intersection S above the ground mark 4. In other words, once the device I has been aligned above the ground mark 4, this height h must be determined with as little expenditure as possible.

In accordance with the invention it is necessary for this purpose to provide a further laser beam path I I which extends at an angle y diverging with respect to the laser beam 10. The angle of divergence y is constant, so that the laser beam 10, the beam path I I and the distance a between two laser beam paths 10, 11 in the height of the ground mark 4 form a measuring triangle from which the height h can be determined easily, as will be demonstrated.

In a first embodiment, which is illustrated in Figure 2, the beam path 11 is generated with the aid of a diffracting element 12. The diffracting element 12 comprises an optically effective structure by means of which a portion of the laser beam 10 is transformed into a circular diffraction pattern 13 which is arranged in a concentric manner with respect to the axis of rotation DA and which is directed in a diverging manner at the ground mark 4 or its 7 surrounding area.

This effect of the diffracting element 12 is achieved, for example, when the diffracting element is produced from a transparent plate, preferably from a glass plate, and is provided with diffraction patterns which consist, for example, of a plurality of dots disposed on concentric circles. These patterns comprise in their centre a region which is highly transparent, so that the passage for the laser beam 10 is as free as possible. For this purpose, the diffracting element 12 can comprise in its centre a cut-out through which the laser beam 10 can pass unhindered.

If, as described hereinunder, the distance a between the laser beam 10 and the laser beam I I or also the diameter d=2a of the large circle of the diffraction pattern 13 is determined in the height level of the ground mark 4, the height h,, which is proportional to the distance a or the diameter d=2a, can be determined therefrom (cf. Figure 2). If the height h2, which corresponds to the distance between the diffracting element and the point of intersection S, is also added to the height hl, then the height h of the point of intersection S above the ground mark 4 is obtained.

In a second embodiment of the invention, illustrated by way of example in Figure 3, two ftirther laser diodes 7.2 and 7.3 are arranged next to the laser diode 7. 1, such that they direct beams at an angle of aO, preferably a=10' into the lens. The lens 8 then images the three laser diodes 7.1, 7.2 and 7.3 via separate collimated beam paths 14 and 15 onto the ground mark 4 or its surrounding area.

Similar to the exemplified embodiment as shown in Figure 2, the distance a between the laser beam 10 and one of the beam paths 14, 15 in the height level of the ground mark 4 is a measurement for the height h3, which corresponds to the distance between the vertex of the angle of divergence y and the ground mark 4. If the height h4, which is fixedly predetermined as far as the device is concerned as the distance between the vertex of the angle of divergence y and the point of intersection S, is added to the height h3, then using the height h the distance of the point of intersection S above the ground mark 4 is obtained.

As an aid for determining the distances a or the diameter d=2a, it is possible to provide a scale 16, illustrated by way of example in Figure 4, which is provided with line markings 17 which are gauged in a length unit. This length unit can be defined using the metric system, so that it is possible to read off measurements in mm. In a particularly 8 preferred embodiment, the gauging can also be provided such that it is possible to read off directly a value which represents the height h.

However, it is extremely advantageous and therefore to be recommended to use a position-sensitive optoelectronic detector with a downstream evaluating device and display device. The latter can, as illustrated in Figure 5, be accommodated together with a CCD line 18 in a flat measuring instrument which is positioned on the ground mark 4 in such a manner that the images of all three laser diodes 7.1, 7.2 and 7.3 lie on the CCD line 18.

The evaluating circuit determines the height h from the distances a whilst evaluating the relationships described above and displays this height on an integrated display 19. The height h can be read off directly and furthermore can be taken into consideration when performing the measurements.

A further embodiment can reside in the fact that the value (height h) determined using the measuring instrument illustrated in Figure 5 is stored and passed for further use to the computer which processes all the measured values determined using the device I to produce the desired measuring result.

In order to align the scale 16 or the measuring device according to Figure 5 in a horizontal manner so that the distance a is measured in the right angle with respect to the axis of rotation DA, it is possible to provide, for example, a boxed bubble level 20. (cf. Figure 4 and Figure 5).

9

Claims

1. Geodetic device having a telescope, whose sighting axis has a common point of intersection with a tilt axis and an axis of rotation about which the telescope can pivot and wherein ftu-thennore a laser arrangement is provided which serves to align the axis of rotation over the ground mark and to determine the height of the point of intersection above the ground mark, wherein a first laser beam extending in the axis of rotation is directed at the ground mark and there is provided at least one further laser beam path which extends in a diverging manner with respect to the first laser beam and includes with the said laser beam an angle y and further comprising a measuring device for determining the distance a, which the diverging laser beam path has in the height of the ground mark from the first laser beam and an evaluating device for calculating the height h from the relationship h-a when the angle y is known.

2. Geodetic device as claimed in claim I wherein the first laser beam is collimated

3. Geodetic device according to claim I or 2, wherein the laser arrangement comprises a housing which is disposed with its longitudinal axis extending radially with respect to the axis of rotation, a laser beam source disposed in the housing, a lens, likewise disposed in the housing, for the purpose of bundling the laser beam and a deflecting element disposed downstream of the lens for the purpose of coupling the laser beam into the axis of rotation and an optical means for generating the second laser beam path which extends in a diverging manner.

4. Geodetic device according to claim 3, wherein a diffracting element comprising an optically effective structure is placed in the laser beam path and through said structure a portion of the laser beam extending in the axis of rotation is transformed into a circular diffraction pattern which is arranged in a concentric manner with respect to the axis of rotation and is directed in a diverging manner at the ground mark or its surrounding area.

5. Geodetic device according to claim 4, wherein the diffracting element is disposed downstream of the deflecting element.

6. Geodetic device according to claim 4 or 5, wherein the diffracting element consists of a transparent plate comprising a structure hologram which is formed from geometric patterns, wherein the patterns are positioned in a central manner with respect to the laser beam and comprise in their centre a maximum brightness.

7. Geodetic device according to claim 6 wherein said geometric devices comprise concentric circles or dots, dot-lines and/or dot areas.

8. Geodetic device according to claim 3, wherein at least one finther laser light source is provided which directs beams at an angle aO' into the lens and is imaged on the ground mark or its surrounding area and whose laser beam path includes with the first laser beam an angle of divergence yz a.

9. Geodetic device according to any of the preceding claims, wherein the measuring device is a scale designed in such a manner that it is possible to read off the distance a visually and the scale is provided with a line marking gauged in a length unit and/or a position-sensitive optoelectronic detector with a downstream evaluating and display device.

10. Geodetic device according to any of the preceding claims, wherein the beam sources are laser diodes which emit beams in the visual wave length range of light.

11. Geodetic device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.